1. Field of the Invention
This invention pertains to tool strings, and particularly to retrievable tool strings used for underbalanced well completions.
2. Related Art
It is often desirable to isolate a portion of a well. For example, a portion of the well may be isolated during insertion or retrieval of a work string. It may also be desirable to isolate a portion of a well during perforation operations, particularly during underbalanced completion operations.
The present invention enables the retrieval of a completion string while maintaining control of a well without having to kill the well (i.e., without having to exceed formation pressure) each time the string is retrieved.